Add "Debugging browser process" chapter.

docs/README.md

@@ -3,6 +3,7 @@
 * [Quick start](tutorial/quick-start.md)
 * [Application distribution](tutorial/application-distribution.md)
 * [Use native node modules](tutorial/use-native-node-modules.md)
+* [Debugging browser process](tutorial/debugging-browser-process.md)
 
 ## API references
 

docs/tutorial/debugging-browser-process.md

@@ -0,0 +1,15 @@
+# Debugging browser process
+
+The devtools of browser window can only debug the scripts of the web pages
+(e.g. the renderer process), in order to provide a way to debug the scripts of
+the browser side (e.g. the browser process), atom-shell has provided the
+`--debug` and `--debug-brk` switches.
+
+## `--debug=[port]`
+
+When this switch is used atom-shell would listen for V8 debugger protocol on
+`port`, the `port` is `5858` by default.
+
+## `debug-brk=[port]`
+
+Like `--debug` but pauses the script on the first line.